A man in Hong Kong is the first with a confirmed reinfection with the novel coronavirus, a new study suggests.
This may be the first major clue to a still-unanswered question about the COVID-19 pandemic: How long does immunity to SARS-CoV-2 last? There have been some previous reports of potential reinfection cases around the globe, but none have been confirmed with definitive testing, according to The New York Times. People who recover from COVID-19 can shed virus fragments for weeks, which can turn up as a positive COVID-19 test results, even when they aren't actually shedding live virus, according to The Times.
But today (Aug. 24), a group of researchers reported on a case of a patient who was infected with two genetically different strains of the coronavirus, months apart, according to a press release from the University of Hong Kong's Department of Medicine. The scientists found that the coronavirus that infected the patient, a 33-year-old-man in Hong Kong, the second time around had 24 different nucleotides, or building blocks, in its gene sequence than the virus that infected him the first time.
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That likely means that the person didn't just continue to shed the same virus months after being infected, according to the study that was just accepted, but not yet published, in the journal Clinical Infectious Diseases.
But this case shouldn't spark widespread fear.
"This is no cause for alarm - this is a textbook example of how immunity should work," Akiko Iwasaki, a professor of immunobiology and molecular, cellular and developmental biology at the Yale School of Medicine, wrote on Twitter.
The patient, who was previously healthy, was first diagnosed with COVID-19 on March 26. During his first infection he had mild symptoms including a cough, sore throat, headache and fever for several days. Though his symptoms subsided, he was hospitalized on March 29 and was discharged on April 14 after testing negative for the virus twice.
Four and half months later, the patient was returning to Hong Kong from Spain via the United Kingdom and tested positive for the virus in a screening at the Hong Kong airport on Aug. 15, according to the report. He was again hospitalized but didn't have any symptoms. "While immunity was not enough to block reinfection, it protected the person from disease," Iwasaki wrote.
Antibody tests showed that the patient did not have any detectable antibody to the coronavirus when he was reinfected but developed detectable antibodies after reinfection.
"This is encouraging," Iwasaki wrote. "While this is a good example of how primary infection can prevent disease from subsequent infection, more studies are needed to understand the range of outcomes from reinfection."
This case of re-infection has "several important implications," the authors wrote in the study. "It is unlikely that herd immunity can eliminate SARS-CoV-2, although it is possible that subsequent infections may be milder than the first infection as for this patient."
COVID-19 will likely continue to circulate in the human population, similar to the coronaviruses that cause common colds, they wrote.
Other implications are that vaccines may not be able to provide lifelong protection against COVID-19 and that vaccines studies should include those who have recovered from COVID-19, the authors wrote.
“What I think is really important is that we put this into context,” Maria Van Kerkhove, the World Health Organization's technical lead for coronavirus response and head of the emerging diseases and zoonoses unit, said during a news briefing in Geneva on Monday (Aug. 24), according to CNN. There's been more than 24 million cases of COVID-19 reported worldwide, and so "we need to look at something like this on a population level."
Van Kerkhove said she was still reviewing the case, according to STAT News. "What we are learning about infection is that people do develop an immune response, and what is not completely clear yet is how strong that immune response is and for how long that immune response lasts."
Originally published on Live Science.